It is known to couple axially-spaced shafts such that a driving shaft (e.g., that of a motor) drives a driven shaft (e.g., that of a pump) through a coupling assembly. One particular type of coupling employs a single or multiple-piece elastomeric element capable of drivably coupling shafts having a limited amount of misalignment with respect to one another. Detailed descriptions of elastomeric coupling assemblies may be found, for example, in U.S. application Ser. No. 09/120,948, filed Jul. 22, 1998 and entitled Tearing Configuration for Flexible Element of Elastomeric Coupling; U.S. application Ser. No. 09/182,147, filed Oct. 29, 1998 and entitled Elastomer Coupling Having Cylindrical Surface Hubs; and U.S. Pat. No. 4,634,400, issued on Jan. 6, 1987. The disclosure of each of these references is incorporated herein by reference insofar as they relate to coupling components, their assembly, and their manner of connecting spaced-apart shafts.
Typically, elastomer coupling assemblies include a hub that is mounted to each shaft (such as by being keyed to each shaft or by being fastened to each shaft via a compression bushing) and a flexible element connected to the hubs. The flexible element is often fastened to the hubs by threaded fasteners such as cap screws, which can connect rigid shoes or sleeves of the flex element to the hubs.
One potentially important consideration in coupling a pair of shafts is the distance between shaft ends (hereinafter "DBSE"). The DBSE is particularly important for back pull-out equipment, such as back pull-out pumps. A back pull-out piece of equipment is typically serviced by swinging out an impeller housing at an end of the pump that includes the rotatable pump shaft. A certain minimum DBSE is required to provide clearance for swinging the impeller housing of the piece of equipment open. The American National Standards Institute (hereinafter "ANSI"), the International Organization for Standardization (hereinafter "ISO"), and the Deutsches Institut fur Normung (hereinafter "DIN") have suggested certain standard DBSE spacings for various applications.
In the past, two types of coupling assemblies have generally been provided. The first conformed to ANSI standard DBSE spacings and the second conformed to ISO and DIN standard DBSE spacings (referred to in the appended claims collectively as "metric" shaft spacings). Thus, each type of coupling assembly permitted incremental DBSE settings within one of either the ANSI or the ISO and DIN standards. ANSI, ISO, and DIN conforming coupling assemblies typically include hubs tapped for ANSI cap screws or for ISO and DIN standard cap screws, respectively.
The different spacings called for in the ANSI and the ISO and DIN standards have long presented a number of problems for coupling manufacturers and suppliers. For example, a provider of coupling assemblies may receive orders for coupling assemblies from companies situated in various countries. To avoid the administrative confusion of tracking which companies or existing field applications in the various countries require ANSI, ISO, or DIN standard couplings, the provider typically provides coupling components (e.g., hubs, cap screws, shoes, and other elements) which conform to ANSI, ISO, and DIN standards for a range of potential DBSE spacings of coupling assembly users. Although couplings are thereby available for applications in which ANSI, ISO or DIN standard spacings exist, this practice increases production costs resulting from manufacturing multiple parts differing only dimensionally (e.g., different hub bore lengths, different hub shoulder widths, etc.); increases shipping fees due to the combined weight of the many parts; creates potential confusion in matching cap screws and hubs having the same threads; and increased inventory cost due the number of coupling components needed to meet the DBSE requirements of ANSI, ISO or DIN standards.
Another limitation of prior art couplings is the ability of the coupling to be easily mounted upon a pair of shafts where each shaft is fully engaged with its respective hub or compression bushing. When the coupling is mounted, it is most desirable that each shaft passes fully through the bores of the respective hubs or compression bushings. Some limited amount of hub overhang is sometimes permissible for straight bore hubs in certain applications, but full hub-to-shaft engagement is preferred for all hub types and is generally required for compression bushed hubs. Also, although the shafts can extend through and past the hubs (into the center of the coupling), this practice is generally not preferred. Preferably, when the hubs are mounted to the shafts, the inner face of each hub is substantially aligned with the end face of its respective shaft. Such alignment allows a used to quickly mount the hubs in their proper positions upon shafts having standardized spacing in such a manner that the flexible element can be quickly connected to the hubs without moving the hubs on the shafts. This arrangement is desired and often required by original equipment manufacturers and is standard industry practice in many applications. Unfortunately however, conventional hubs which mount upon ANSI--spaced shafts are just described (and which are thereby properly spaced for flexible element connection) generally do not also mount upon ISO or DIN-spaced shafts without some degree of shaft overhang or overextension. A coupling having hubs which can be mounted upon the shafts and aligned with the shaft ends in ANSI, ISO, and DIN spacing increments would be a significant advancement in the art.
In light of the above problems and limitation of prior art couplings, a need exists for a coupling assembly which is easy to assemble and manufacture, adjustable to accommodate incremental DSBE settings in each of the ANSI, ISO, and DIN spacing standards, and which does so preferably with hubs and shaft ends aligned in multiple spacing standards, without increased coupling parts and without the need for coupling components dedicated for each standard. Each one of the preferred embodiments of the present invention described below accomplishes one or more of these results.